This disclosure relates to an array of vertical diodes to select one of a plurality of resistively switching memory cells and a method for forming the array of diodes.
In resistively switching memory cells, for example phase change random access memory (PCRAM) or magneto resistive random access memory (MRAM), the information is stored in a volume of switching active material, wherein the switching active material may switch between two states. In a first state the switching active material may have a high resistivity, i.e., a low conductivity, and a lesser resistivity, i.e., a higher conductivity, in a second state. Accordingly the information of a bit may be assigned to a PCRAM cell, wherein the state of the cell reflects the status of the bit. Although the disclosure is described for PCRAM cells in the following, the structure and methods can be used for any random access memory including diodes as selection means.
For reading a resistively switching memory cell the resistance of the volume of resistively switching material is sensed, i.e., the conductivity is sensed. This can be achieved for example by applying a predefined voltage to the cell and sensing the amplitude of the current flowing through the cell. For switching the state of a resistively switching memory cell a high current is sent through the volume of switching active material in order to heat and subsequently change the material from a one state to the other. Accordingly a selection diode included in the cell thus should be able to send a strong current through the cell.
To be cost competitive, a small cell size and a cost competitive process is required for a memory product including resistively switching memory cells. In conventional architectures a 1D1R assignment is used, i.e., one diode (D) for selecting one resistively switching memory element (R) from a plurality of memory elements.
For these and other reasons, there is a need for the present invention.